The invention relates to a metering pump assembly for admixing a fluid reduction agent in an exhaust gas flow.
With auto-igniting internal combustion engines, nitrous oxides arise on operation with excess oxygen, which is the case the majority of operating conditions, and specifically with direct injection into the main combustion space, as is typical with diesel motors. It is known to supply a reduction catalyser to the exhaust gas flow, in order to reduce these nitrous oxide emissions. Usually, an aqueous urea solution as a reduction agent is supplied to the exhaust gas in a finely distributed manner before entry into the catalyser. Thereby, the supplied urea quantity is to be matched as exactly as possible to the combustion process, in order to ensure an as complete as possible reduction within the catalyser, and on the other hand to avoid an excess of urea.
A special metering pump for metering and supplying the reduction agent to the exhaust gas flow is known from EP 1 435 458 A1. With this metering pump, the supplied reduction agent is mixed or subjected to pressurized air in the metering pump assembly before the supply to the exhaust gas flow. The known metering pump assembly, to the outside comprises four connections, specifically for a suction conduit, for a return conduit, for a pressurized air supply as well as for the conduit to an injection nozzle in the exhaust gas system. All essential components for operation of the metering pump and of the premixing device for mixing the reduction agent with pressurized air are integrated into the metering pump assembly.